The objective of this application is to obtain a FACStar PLUS flow cytometer system. Eight investigators funded by 11 USPHS research grants will share this instrument for purposes of phenotyping and sorting specific subpopulations of cells. Project I aims at understanding the signal requirements and the biochemistry of early events involved in normal T cell activation. The basis of the activation defect in patients with T cell immunodeficiency will be studied. Project II examines the ontogeny of B cells following bone marrow transplantation. Project III studies the role of immunoregulatory abnormalities in the pathogenesis of vasculitis during Kawasaki Syndrome (K.S.) and characterizes the subpopulation of lymphocytes which contain the retrovirus associated with K.S. In project IV, the presence and function of T cells bearing Fc receptors for IgE (Fc epsilon R) will be assessed in clinical conditions associated with elevated IgE levels and the T cell Fc epsilon R will be characterized. Project V studies anti-idiotypic (alpha Id) antibodies from patients with Cl inhibitor deficiency and B cell lymphoproliferative disorders. The presence of alpha Id and of Cl on the B cells will be quantitated. Project VI is concerned with identification of new DNA coding sequences within the class III region of human MHC. New gene products will be located on transfected cells. Project VII will use the cell sorting capacity of the FACStar PLUS to isolate double stranded DNA binding B cells and analyze the genetic factors which give rise to anti-DNA antibodies in systemic lupus erythematosus. Project VIII studies the cell expression of leukocyte adhesion molecules (Leu-CAM) in normals and in patients with Leu-CAM deficiency, Project IX characterizes the stages of immunoglobulin gene rearrangement in B cells from patients with X-linked agamma-globulinemia (XLA). Transfected XLA B cells expressing VH gene products will be isolated and used to identify the defective gene projects. In Project X, the FACStar will be used to evaluate expression of new cell surface antigens following infection with respiratory syncytial virus. Project XI will study the effectiveness of new drugs in the treatment of AIDS. The FACStar will be used for evaluating changes in lymphocyte phenotypes of patients on various treatments. At present, each of the 8 investigators has only limited access to a flow cytometer or cell sorter. It is anticipated that each of these USPHS funded research projects will benefit from the acquisition of this instrument.